Saddle design per MOSS 1

[VPbris]

Hi,

I`m trying to figure out two steps on the design of support saddles using MOSS`s Pressure Vessel Design Manual, I`m using the 4th edition,

On Procedure 4-11, pages 270 and 271 (Page 181 on 3rd edition), in order to determine the baseplate thickness it first determines the bending moment (M), anyone has an idea why it is equal to QF/8 ? According to my calculations it should be QF/2.

Then again when determining M for offset web, M is now w*l²/6, and the unit for that is Force, not Force*length.

I`m attatching page 181 from 3rd edition.

A is the baseplate length
F is the baseplate width
Q is the load per saddle
Fb is allowable bending stress
fb is calculated bending stress

 

[JStephen]

Treating half the base plate as a cantilever, load is Q/2 (load on one half) times F/4 (half the cantilever length) = QF/8.
On the second item, load is wL/2, centroid is L/3, product is WL^2/6.

 

[DSB123]

VPbris,
If you do not understand the procedures in Moss then do not use them!!!